8-Bit Synchronous Counter with Carry-Lookahead
High-frequency processors and network routers require timers that do not bottleneck the system clock. A standard synchronous counter uses a ripple-carry AND chain that creates an escalating critical path delay. Carry-lookahead principles reduce this critical path by generating toggle terms in parallel.
Implement an 8-bit synchronous up-counter using two-level AND-OR logic for all carry and toggle terms. The counter state Q increments by 1 on every clock cycle when en is high. When rst is high, the counter synchronously resets to 0.
| rst | en | Q_next | |-------|------|----------| | 1 | 0 | 0 | | 1 | 1 | 0 | | 0 | 0 | Q | | 0 | 1 | Q + 1 |
Constraints
- Limit the logic path between any flip-flop output
Qand any toggle inputTto a maximum of two gate levels. - Do not use a serial ripple-carry AND chain between stages.
- Generate shared partial product terms to drive the upper bits.
- Use only basic logic gates and standard flip-flops.
Topics
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